1. Field of the Invention
This invention relates to new and useful improvements in methods or reduction in power consumption in fluorescent lamps and to attachments for use in electric circuits for fluorescent lamps which accomplish such reduction in power consumption.
2. Brief Description of the Prior Art
Numerous stores, offices and homes employ fluorescent lighting fixtures to provide desired illumination. Many of these fluorescent lamp fixtures employ the long cylindrical fluorescent type lamp known as the "rapid start" type which contains heater filaments. Such lamps are operated in the fixture individually or in groups of two or more, electrically connected in series effectively and operated from a high reactance transformer and capacitor combination, sometimes referred to as a "ballast," which provides the high starting voltages required by these fluorescent type lamps the current limited lower operating voltages and the filament current and voltages. By design the lamps and the ballasts are matched together so that the lamps operate at maximum efficiency and hence, by design, a certain electrical current effectively flows through the lamp circuit to provide full lamp brightness. Electrical power is obtained via the building wiring from the local power company or utility and is supplied to the ballast input.
Most fluorescent lighting systems are of the rapid start type in which the lamp electrodes are preheated for a short time by low voltage followed by applying high voltage to fire the lamp. Such systems utilize a rapid start ballast having a step down transformer for heating the lamp electrodes and autotransformer for firing the lamp. The ballast conventionally has one or more capacitors connecting the secondary winding of the autotransformer to the secondary winding or windings of the step down transformer and resistors connected in parallel with each such capacitor. The ballast, including the transformers, capacitors and resistors, is usually encapsulated in resin, asphalt, or plastic with color coded leads extending therefrom for connection to the power source and to the fluorescent lamp tube.
For many years, there has been a conservation move to reduce electrical consumption. In particular, some electrical utilities have been requiring consumers, such as the industrial, store and factory users, to reduce electrical power consumption by 15% or more or suffer a financial penalty or, possibly, cut-off of electrical service. To meet this requirement, business has resorted to many expedients resulting in some such savings with unavoidable individual inconvenience. Thus the hot water has been turned off; the temperatures for air conditioning are fixed for a higher than normal temperature; heating is limited; and, most relevant to the present invention, the lights are "turned off".
If each fluorescent lamp fixture were controlled by a single associated wall-mounted "on-off" switch and only selected lamp units were turned off, the practice of that expedient and the concurrent power savings is simple. In practice however, long "banks" of fixtures are controlled by a single "on-off" switch. Hence if the switch is turned to "off" an entire area may be placed in darkness. Obviously that condition is impractical in a business or factory.
Instead the procedure which has been adopted is the simple expedient of removing alternate pairs of the fluorescent lamps from the overhead fixtures. In a sense this cuts down the illumination in an area to one-half of some other fraction less than previously obtained with all lamps in operation. Thus although lighting is reduced, the area remains sufficiently illuminated to permit persons to continue performance of their duties.
In the example given, although the amount of illuminations is reduced in half by removal of half of the lamps, the electrical consumption it is found is not reduced in half as logic might suggest. What is over-looked in the practice of this expedient is although the "electrical load," i.e., the fluorescent lamps, is removed, the ballast transformer remains connected in circuit in the electrical power system. Consequently the primary of the ballast remains in the electrical system as an inductively reactive electrical load. As is known to those skilled in the art, the magnetic hysteresis action inherent in the iron core of the transformer consumes some minor amount of power, technically known as "core loss." In addition, the reactive current supplied the ballast transformer is of a significant level.
As is familiar to those skilled in the art, large reactive currents flowing in the on-premises electrical system lines create resistive heating losses therein and thus waste electrical energy. Not only is this undesirable on the premises but it is also undesirable from the standpoint of the utility company, inasmuch as these large reactive currents must be fed into the electrical lines over the utility company's electrical lines and distribution transformers and this too can be overheated. For example, in one test, two 40-watt rapid-start type lamps were removed from their sockets in the lamp fixtures and 38 volt-amperes are measured at the ballast input. This volt-ampere is lower than the normal level of 102 volt-amperes, but is larger than the desired reading of zero if the ballast input was disconnected from the power line. The reader may make reference to the literature concerning "power factor correction" and measures normally taken by the utility companies and others to eliminate reactive currents of this type from electrical distribution lines and maintain the power factor of the line current at approximately "1." Thus not only is the consumer deprived of desired light, but savings of electricity are not as great in practice as one might expect from that privation.
If the electrical connections to the ballast were disconnected from the power line, the problem of continued reactive current is avoided entirely. However to do so is a more difficult task than simply removing the fluorescent lamps from their sockets and also makes it more difficult to return those lamps to service.
In recent years several improvements have appreared in the patent literature and some have appeared on the market for reducing electrical energy consumption in fluorescent lighting systems.
Luchetta U.S. Pat. No. 3,954,361 discloses an attachment for use in two-lamp fluorescent lighting fixtures comprising an isolation transformer and a capacitor connected across the transformer to reduce power consumption of the fluorescent lamps.
Abernathy U.S. Pat. No. 4,135,115 discloses an attachment comprising an isolation transformer and two capacitors connected across the transformer on opposite sides, and a resistor connected in parallel with one of the capacitors to reduce power consumption of the fluorescent lamps.
Other U.S. patents, viz. U.S. Pat. Nos. 4,082,981; 4,163,176; 4,256,993; 4,339,690; 4,388,564; 4,435,670; and 4,501,992 disclose other variations on the basic circuit of Luchetta, i.e. an isolation transformer and a capacitor connected across the transformer to reduce power consumption of the fluorescent lamps.
This prior art and the products commercially available today suffer from the deficiency that they produce a triangular wave pattern output to the lamps and do not include resettable means for shutting down the system on failure of the ballast transformer or ballast power factor capacitor.